Thermal barrier coating systems (TBCs) for high performance gas turbines are one of the most demanding applications for advanced ceramics in modern technology. These engineered surfaces are multifunctional, providing both thermal and environmental protection to the structural metallic components, but the thermal barrier itself is also subject to multiple requirements that go beyond its basic function of thermal insulation to influence both its durability and performance. Zirconia partially stabilized with 7±1wt%Y2O3 (7YSZ) has been the standard material for TBCs since their commercial insertion. The demands for increased engine performance and fuel flexibility in advanced gas turbines translate into higher temperatures and more aggressive operating environments for TBCs, driving the search for alternate materials, most of which retain ZrO2 as the base oxide with rare earth and/or or transition metal additions. Because a key element in the durability of current TBCs is their non-transformable tetragonal (t’) structure, which is metastable in its pristine condition, one must tread carefully in the design space to achieve desired targets in functionality such as lower thermal conductivity or increased corrosion resistance, while maintaining adequate toughness, phase stability, compatibility with the underlying thermally grown oxide (TGO) and morphological stability of the strain-tolerant microstructure. This presentation will provide an overview of the field, highlighting key issues and examples of opportunities for fundamental research with direct impact on this critical energy technology.
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